Pneumatic tyre

Abstract: A pneumatic tyre has a block pattern which is divided by a centre main groove extending straight on the tyre equator, two outer main grooves extending straight outside the centre main groove, inner lateral grooves crossing between the centre and outer main grooves, and outer lateral grooves crossing between the outer main grooves and tread edges so as to make two inner block rows and two outer block rows. The outer lateral grooves cross the outer main grooves, and the inner lateral grooves cross the centre main groove at an inclination opposite to an inclination direction of the outer lateral grooves. The block pattern is satisfied with the following relation; 0.3 ≦ Ni/No ≦ 0.7 0.1W ≦ WG1 ≦ 0.17W 0.1W ≦ WG2 ≦ 0.17W 0.3W ≦ WBi ≦ 0.6W 0.3W ≦ WBo ≦ 0.6W 1.3 ≦ Pgi/WBi ≦ 3.5 0.5 ≦ Pgo/WBo ≦ 1.2

Description: The present invention relates to a pneumatic tyre capable of reducing pass-by noise while maintaining steering stability, wet grip performance and other running performances. As vehicle speeds are getting higher along with advancement of automotive technology in recent years, the vehicle running noise is increasing, and its control is demanded. In the tread of the tyre, a block pattern, typically shown in Fig. 4, is formed by a plurality of circumferential grooves (a), (b) extending continuously in the tyre circumferential direction and multiple lateral grooves (d), (e) crossing these circumferential grooves. Therefore, when running in rain, the water between the tread surface and the road surface is discharged through these grooves, and the wet grip performance is enhanced. When such lateral grooves are provided in a multiplicity, the air compressed between the tread surface and the road surface passes through the grooves suddenly, and occurs intermittently, which causes a noise called a pumping noise. Such noise is often noted in block pattern tyres having multiple lateral grooves. To suppress such noise, it has been attempted to lower the speed of the air passing the lateral grooves by 1. decreasing the sectional area of the lateral grooves, or 2. bending the lateral grooves. By these measures, although the noise is slightly reduced, measure 1 causes a loss in grip performance, especially wet grip performance, and measure 2 causes uneven wear on the sides of the lateral grooves, thereby lowering the travelling performances and durability of the tyre. It is hence a primary object of the invention to present a pneumatic tyre capable of reducing the pass-by noise while maintaining the running performances. The present inventor has discovered: (1) The noise frequency is dispersed and the noise is lessened by differing the pitch of blocks between the block rows. (2) The wet performance is enhanced by increasing the sectional area of the main grooves extending in the circumferential direction. (3) The turning performance is enhanced by setting the block pitch in the inner block rows larger than the outer block pitch so as to make the shape of the outer blocks oblong, while strengthening the grip force and brake performance. (4) The water discharge performance is enhanced and noise generation is further suppressed by smoothly continuing between the lateral grooves in the inner block rows and lateral grooves in the outer block rows. According to the present invention, a pneumatic tyre comprises a tread, said tread having a centre main groove extending on the tyre equator, two outer main grooves disposed outside the centre main groove in the tyre axial direction, inner lateral grooves crossing between the centre main groove and the outer main grooves and outer lateral grooves crossing between the outer main grooves and tread edges so as to divide the tread surface into two inner block rows of inner blocks divided by the centre main groove, one of the outer main grooves and inner lateral grooves and two outer block rows of outer blocks divided by one of the outer main grooves, one of the tread edges and the outer lateral grooves; said centre and outer main grooves have parallel groove edges on the tread surface extending substantially straight in the tyre circumferential direction, each of said inner lateral grooves crossing the groove edge of the centre main groove at an inclination opposite to an inclination direction of the outer lateral grooves, characterized by each of said outer lateral grooves crossing the groove edge of the outer main grooves at an inclination, and the following relation being established: 0.3 ≦ Ni/No ≦ 0.7 0.1W ≦ WG1 ≦ 0.17W 0.1W ≦ WG2 ≦ 0.17W 0.3W ≦ WBi ≦ 0.6W 0.3W ≦ WBo ≦ 0.6W 1.3 ≦ Pgi/WBi ≦ 3.5 0.5 ≦ Pgo/WBo ≦ 1.2 where: Ni is the number of inner blocks in one inner block row: No is the number of outer blocks in one outer block row: WG1 is the centre groove width corresponding to the length between the groove edges of the centre groove in the tyre axial direction: WG2 is the outer groove width corresponding to the length between the groove edges of the outer groove in the tyre axial direction: WBi is the inner block width corresponding to the length between the groove edges of the centre main groove and the outer main groove in the tyre axial direction: WBo is the ground contacting width of the outer blocks corresponding to the length between the ground contacting edge and the groove edge of the outer main groove in the tyre axial direction: Pgi is the pitch length of the inner lateral grooves in the circumferential direction: Pgo is the pitch length of the outer lateral grooves in the circumferential direction: and W is a ground contacting half width from the tyre equator to the one ground contacting edge. The ratio Ni/No of the number Ni of the inner blocks and the number No of the outer blocks is from 0.3 to 0.7. Therefore, when running, a deviation occurs in the noise frequency between the pumping noise generated from the inner block rows and the pumping noise generated from the outer block rows. By this deviation, the range of the noise is diffused, and the irritating noise to the ear hearing a peak at the 1000 Hz characteristic of the pumping noise is diffused, so that it may be lessened and alleviated. Still more, by defining the ratio Ni/No within the above mentioned range, the peak frequency of the noises generated from both inner and outer blocks can be separated, and generation of resonant sounds such as beats is eliminated. If less than 0.3, the length of the outer blocks in the circumferential direction becomes too long, thereby impairing the grip performance in dry and wet condition. But if it exceeds 0.7, the noise generated from the outer block rows and the inner block rows are resonant to each other, and the effect to reduce the pass-by noise is not achieved. The centre and outer main grooves have their groove widths WG1, WG2 in a range of 0.1 to 0.17 times the ground contacting half width W, and hence these main grooves maintain the water discharging performance. If less than 0.1 times, the water discharge performance is low in running in rain, and the wet grip performance, wet braking and other wet running performances are impaired. But if exceeding 0.17 times, the actual ground contact area becomes smaller, and the ground contact pressure is increased, wear of the tread surface is accelerated, and durability is lowered. Further, the inner block width WBi and the ground contacting width WBo of the outer blocks are defined in a range of 0.3 to 0.6 times the width W. This is intended to equalise the ground contacting area of the inner and outer blocks, and by equalising the ground contacting areas of the both block rows as closely as possible, the sound levels of the noise generated in both block rows come closer to each other, so that the sound can be smoothed. If either block is less than 0.3 times or exceeds 0.6 times, the balance of the noise levels produced from both block rows is broken, and the effect of lowering the noise and the effect of smoothing the noise both become smaller. Furthermore, the ratio Pgi/WBi of the pitch length Pgi of the inner lateral grooves to the inner block width WBi is defined in a range of 1.3 to 3.5. Therefore, the inner blocks are formed as slender blocks having a length in the circumferential direction longer than the width dimension are formed. This enhances the traction force. If the ratio Pgi/WBi is less than 1.3, the traction performance is lowered. If it exceeds 3.5, to the contrary, the interval between the inner lateral grooves is too long and the water discharge performance is lowered, thereby impairing the wet grip performance and wet braking performance. In addition, the ratio Pgo/WBo Pgo/WBo of the pitch length Pgo of the outer lateral grooves to the ground contacting width WBo of the outer blocks is defined as in a range of 0.5 to 1.2. Therefore, the ground contacting surface of the outer blocks is an oblong shape having a length in the circumferential direction shorter than the width, or a square, or a slender shape similar to a square. By defining the ground contacting surface of the outer blocks at the specified ratio, the cornering performance factors such as running stability and steering stability are maximised. If the ratio Pgo/WBo is less than 0.5, the traction performance in straight running is impaired, and if exceeding 1.2, the cornering performance is inferior. In the invention, the individual features as mentioned above are coupled and united organically, and the pass-by noise is reduced while maintaining the running performances in dry and wet state. An embodiment of the present invention will now be described, by way of example, referring to the attached diagrammatic drawings, in which: Fig. 1 is a developed plan view showing a tread pattern of an embodiment of the invention; Fig. 2 is a sectional view of a tyre; Fig. 3 is a developed plan view showing a tread pattern of another embodiment of the invention; and Fig. 4 is a developed plan view showing a tread pattern of a conventional tyre. A pneumatic tyre 1 comprises a tread 2 with a block pattern, two side walls 13 each extending inwardly in the tyre's radial direction from both ends of the tread 2 and two beads 14 one located at the inward end of each sidewall 13. The pneumatic tyre 1 is, also, reinforced by a toroidal carcass 16 extending from the tread 2 through the side walls 13 and turned up around the bead core 15 of the bead 14, a belt layer 17 disposed radially outside the carcass 16, and a bead apex rubber 18 extending radially outwardly from the bead core 15 between the carcass main body and carcass turned up portion. The carcass 16 is composed of one carcass ply in this embodiment. The carcass ply has its carcass cords arranged at an angle of 80 to 90 degrees to the tyre equator C and covered with topping rubber. Nylon, polyester, rayon, aromatic polyamide, or other organic fibre cords may be used as carcass cords. The belt layer 17 is composed of two belt plies 17A. The belt plies 17A have belt cords such as nylon, polyester, rayon, aromatic polyamide, or other organic fibre cords or steel cords, which are arranged in mutually intersecting directions between plies. The tread 2 has a centre main groove GI extending on the tyre equator C and two outer main grooves GO disposed one on either side of the centre main groove GI so as to divide the tread surface 2A into a pair of inner ribs RI, RI between the centre main groove GI and the outer main grooves GO, and a pair of outer ribs RO, RO between the tread edges E and the outer main grooves GO. The centre main groove GI has groove edges 3, at which the opposing groove walls intersect with the tread surface 2A, extending substantially straight in the tyre circumferential direction. Each of the outer main grooves GO, also, has groove edges 4, at which the opposing groove walls intersect with the tread surface 2A, extending substantially straight in the tyre circumferential direction. Further, the inner ribs RI are provided with inner lateral grooves gi crossing the adjoining groove edges 3, 4 of the centre and outer main grooves GI, GO so as to form inner block rows LI of inner blocks BI arranging in the circumferential direction. The outer ribs RO are provided with outer lateral grooves go crossing the adjoining tread edges E and groove edges 4 of the outer main grooves GO so as to form outer block rows LO of outer blocks BO arranging in the circumference direction. In the pneumatic tyre 1, the ground contacting surface of tread 2 where the tread surface 2A contacts the road surface in the normal state of tyre is defined as the ground contacting region. And the distance between the ground contacting edge F, which is the edge remotest from the tyre equator C at the periphery of the ground contacting region in the tyre axial direction, and the tyre equator C is defined as the ground contacting half width W. The above mentioned normal state of the tyre is the state when that tyre is mounted on the regular rim officially approved for the tyre by, for example JATMA, TRA, ETRTO and the like, and inflated to its regular internal pressure as officially specified as the maximum air pressure in Air-pressure/Max.-loads Table by, for example JATMA, TRA, ETRTO and the like, and loaded with a normal tyre load officially specified as the maximum load for the tyre in Air-pressure/Max.-loads Table by, for example JATMA, TRA, ETRTO and the like. In such a block pattern, the centre groove width WG1 between the opposing groove edges 3, 3 of the centre main groove GI in the tyre axial direction is defined in a range of 0.1 to 0.17 times the ground contacting half width W, and the outer groove width WG2 between the opposing groove edges 4, 4 of the outer main grooves GO in the tyre axial direction is set in a range of 0.1 to 0.17 times the ground contacting half width W, same as in the case of the centre main groove GI. However, it is not necessarily required to equalise the width dimensions of WG1 and WG2. Incidentally, the groove depth of the centre and outer main grooves GI, GO is preferred to be in a range of 0.12 to 0.2 times the ground contacting half width W. The outer lateral grooves go extend from the tread edge F axially inwardly along a mildly curved line, in this embodiment, and intersect the groove edge 4 of the outer main grooves GO at an inclination. The inclination angle  1 at the acute angle side intersecting the groove edge 4 is set in a range of 30 to 90 degrees. The outer lateral grooves go are provided in each outer rib RO spaced at nearly equal pitch in the circumferential direction, and extend parallel to each other in the same direction and at the same inclination angle  1. In this embodiment, the outer lateral grooves go are provided in one outer rib RO and the outer lateral grooves go provided in the other outer rib RO are a point symmetrical arrangement to each other, therefore the outer lateral grooves go of one outer rib RO and the outer lateral grooves go of the other outer rib RO are inclined in the same direction. The inner lateral grooves gi are smoothly consecutive to the lateral grooves go of the adjacent outer block row LO through the outer main grooves GO. And the inner lateral grooves gi have a bending point 5, at which the inner lateral groove gi inverts the inclination direction to the tyre circumferential direction, in the inner rib RI. That is, the inner lateral groove gi is composed of a portion 5A, which is disposed axially outside the bending point 5 and smoothly consecutive to the adjacent lateral groove go, and a portion 5B, which is disposed axially inside the bending point 5 and inclined in an opposite direction to the portion 5A. The inner lateral grooves gi intersect the groove edge 3 of the centre main groove GI at the point M at an inclination, and the inclination angle  2 at the acute angle side is defined in the range of 15 to 70 degrees. The inner lateral grooves gi are provided at every other outer lateral groove go, and disposed nearly at the same pitch in the circumferential direction in the same direction, and at the same inclination angle  2 to the centre main groove GI. The inner lateral grooves gi pass through, in this embodiment, the centre main groove GI, and are terminated at the point N in the inner blocks BI of the adjacent inner block row LI. By varying the direction of the inner lateral grooves gi at the bending point 5, the flow of air passing the inner lateral grooves gi is lowered at the bending point 5, and hence the pass-by noise generated by the lateral grooves gi may be suppressed. On the other hand, the inner lateral grooves gi are smoothly consecutive to the outer transverse grooves go, and hence the water flowing in the inner lateral grooves gi can flow into the outer lateral grooves go, so that it may be discharged efficiently from the outer lateral grooves go. Moreover, since the angle  2 is 15 to 70 degrees, when the direction of the portion 5B is set to the tyre rotating direction, the water in the inner ribs RI being highest in the grounding pressure may be passed efficiently. Therefore, hydroplaning on a wet road can be prevented, and the running stability and braking performance on wet road can be enhanced. If the angle  2 is less than 15 degrees, the angle of the inner blocks BI formed by the central main groove GI and the inner lateral grooves gi is acute, and uneven wear is likely to occur in the acute part. When the angle  2 is over 70 degrees, the capacity of collecting the water of the inner lateral grooves gi is lowered, and the water discharge performance is inferior. Furthermore, since the angle  1 of the outer lateral grooves go is defined within 30 to 90 degrees, the water flowing in from the outer lateral grooves go and inner lateral grooves gi is efficiently discharged toward the both sides in the tyre axial direction, so that the wet performance is enhanced. If the angle  1 is less than 30 degrees or more than 90 degrees, the water discharge performance by the outer lateral grooves go is lowered, and the wet performance drops. The groove depth of the inner and outer lateral grooves gi, go is desired to be 0.7 to 1.0 times the groove depth of the centre and outer main grooves GI, GO. Further, in the block pattern, the width WBi of the inner block BI, that is, the length in the tyre axial direction between the groove edge 3 and 4 adjacent to each other is set in the range of 0.3 to 0.6 times the ground contacting half width W, and the ground contacting width WBO of the outer block BO, that is, the length in the tyre axial direction between the groove edge 4 and the ground contacting edge F adjacent to each other is set in the range of 0.3 to 0.6 times the ground contacting half width W. In the inner ribs RI, the ratio Pgi/WBi of the pitch length Pgi of the inner lateral groove gi in the circumferential direction to the inner block width WBi is set in a range of 1.3 to 3.5, thereby shaping the inner block BI to be long in the circumferential direction. In the outer ribs RO, the ratio Pgo/WBo of the pitch length Pgo of the outer lateral groove go in the circumferential direction to the ground contacting width WBo of the outer block BO is set in the range of 0.5 to 1.2, thereby shaping the ground surface of the outer block BO as an oblong or slender shape close to a square in the circumferential direction. The ratio Ni/No of the number No of outer blocks BO in one outer block row LO to the number Ni of BI in one inner block row LI is 0.5, in this embodiment, because the inner lateral grooves gi are provided at every other outer lateral groove go. However, the ratio Ni/No is permitted to be 0.3 to 0.7. By setting the ratio Ni/No within the above mentioned range, a deviation of the noise frequency occurs between the pumping noise generated from the inner block rows and the pumping noise generated from the outer block rows so diffusing the range of the noise. Also the peak frequency of the noise generated from each of the inner and outer blocks can be separated, and generation of resonant sound such as a beat is eliminated. In this embodiment, the inner block BI and outer block BO are provided with fine grooves 6, 7 respectively, each extending linearly in the tyre circumferential direction. The groove widths WG3, WG4 of these fine grooves 6, 7 are preferred to be in the range of 0.01 to 0.07 times the ground contacting half width W. Such fine grooves 6, 7 improve further the water discharging performance of the tread surface, thereby enhancing the wet running performance. And also in dry running, the gripping force of the blocks BI, BO is stronger, and the traction performance and braking performance can be enhanced. When the groove width WG3, WG4 are less than 0.01 times the ground contacting half width W, effect on the water discharge performance is not recognised, and if exceeding 0.07 times, the ground contacting area of the blocks BI, BO is smaller, and the wear resistance deteriorates. Fig. 3 shows a block pattern of other embodiment of the invention. In Fig. 3, the inner lateral grooves gi extend substantially straight without the bending point 5, and are smoothly consecutive to every other adjacent outer lateral groove go. The outer lateral grooves go of one outer rib RO are inclined at a same angle and in a same direction with the outer lateral grooves go of other outer rib RO. Trial products of tyres (embodiments) in a tyre size of 195/60, the composition as shown in Figs. 1, 2, and specification as shown in Table 1 were fabricated, and their performances were tested. Tyres of conventional patterns (comparative examples) shown in Fig. 4 were also tested, and the performances were compared. The test methods were as follows. 1) Pass-by noise An actual car coasting test specified in JASO C606 was conducted on and a four-wheel drive of 1500 class on a straight test course. A distance of 50 m was driven at a passing speed of 60 km/h, and at the centre point of this course, a microphone was set up at a distance of 7.5 m from the running centre line at a height of 1.2 m from the road surface, the pass-by noise was measured, and expressed as an index with the prior art taken as 100. The greater the figure, the smaller the pass-by noise. 2) Brake performance Using the same car as in 1), the test road was driven at a speed of 60 km/h, and the vehicle was suddenly braked by locking all four wheels. The stopping distance was measured, and indicated as the index with the prior art taken as 100. The greater figure means the better performance. 3) Turning performance Using the same car as in 1), a curved road with radius of 50 m was followed. The turning performance was evaluated by the time required and the driver's feeling, and indicated as an index with the prior art taken as 100. The greater figure means the better performance. 4) Wet performance Using the same car as in 1), the speed was gradually accelerated from zero on a skid pad road with a water depth of 5 mm. The speed when slipping began to take place was expressed as the index with comparative example 1 taken as 100. The greater figure means the better performance. 5) Steering stability Driving the test course by using the same car as in 1), it was judged by the driver's feeling, and indicated as an index with the prior art taken as 100. The greater figure means the better result. The test results are shown in Table 1. As a result of tests, the embodiments were proved to be lowered in pass-by noise and enhanced in the running performances as compared with the prior art. Embodiment Comparative The center groove width (WG1) 9.0 mm 9.0 mm The outer groove width (WG2) 10.5 mm 10.5 mm The fine groove width of inner block (WG3) 1.2 mm 1.2 mm The fine groove width of outer block (WG4) 2.7 mm 2.7 mm The ground contacting half width (W) 72.0 mm 72.0 mm Ratio WG1/W 0.125 0.125 Ratio WG2/W 0.153 0.153 Ratio WG3/W 0.017 0.017 Ratio WG4/W 0.038 0.038 The inner block width (WBi) 25.0 mm 25.0 mm The grounding width of outer block (WBo) 43.0 mm 43.0 mm Number of inner blocks in one block row (Ni) 33 66 Number of outer blocks in one block row (No) 66 66 Ratio Ni/No 0.5 1 Angle ( 1) 50 deg.±5° ------ Angle ( 2) 35 deg.±5° ------ Pass-by noise (index) 120 100 Brake performance (index) 115 100 Turning performance (index) 115 100 Wet performance (index) 115 100 Steering stability (index) 120 100

Claims: A pneumatic tyre comprising a tread (2), said tread (2) having a centre main groove (GI) extending on the tyre equator, two outer main grooves (GO) disposed outside the centre main groove (GI) in the tyre axial direction, inner lateral grooves (gi) crossing between the centre main groove (GI) and the outer main grooves (GO) and outer lateral grooves (go) crossing between the outer main grooves (GO) and tread edges (E) so as to divide the tread surface (2A) into two inner block rows (LI) of inner blocks (BI) divided by the centre main groove (GI), one of the outer main grooves (GO) and inner lateral grooves (gi) and two outer block rows (LO) of outer blocks (BO) divided by one of the outer main grooves (GO), one of the tread edges (E) and the outer lateral grooves (go), said centre main groove (GI) and outer main grooves (GO) have parallel groove edges (3,4) on the tread surface extending substantially straight in the tyre circumferential direction, each of said inner lateral grooves (gi) crossing the groove edge (3) of the centre main groove (GI) at an inclination opposite to an inclination direction of the outer lateral grooves (go), characterized by each of said outer lateral grooves (go) crossing the groove edge (4) of the outer main grooves (GO) at an inclination, and the following relation being established: 0.3 ≦ Ni/No ≦ 0.7 0.1W ≦ WG1 ≦ 0.17W 0.1W ≦ WG2 ≦ 0.17W 0.3W ≦ WBi ≦ 0.6W 0.3W ≦ WBo ≦ 0.6W 1.3 ≦ Pgi/WBi ≦ 3.5 0.5 ≦ Pgo/WBo ≦ 1.2 where: Ni is the number of inner blocks (BI) in one inner block row (LI): No is the number of outer blocks (BO) in one outer block row (LO): WG1 is the centre groove width corresponding to the length between the groove edges (3) of the centre main groove (GI) in the tyre axial direction: WG2 is the outer groove width corresponding to the length between the groove edges (4) of the outer main groove (GO) in the tyre axial direction: WBi is the inner block width corresponding to the length between the groove edges of the centre main groove (GI) and the outer main groove (GO) in the tyre axial direction: WBo is the ground contacting width of the outer blocks (BO) corresponding to the length between the ground contacting edge (F) and the groove edge (4) of the outer main groove (GO) in the tyre axial direction: Pgi is the pitch length of the inner lateral grooves (gi) in the circumferential direction: Pgo is the pitch length of the outer lateral grooves (go) in the circumferential direction: and W is a ground contacting half width from the tyre equator (C) to the ground contacting edge (F). A pneumatic tyre according to claim 1, characterised in that the inner lateral grooves (gi) pass through the centre main groove (GI, and are interrupted in the inner blocks (BI) of the adjacent inner block row (LI). A pneumatic tyre according to claim 1 or 2, characterised in that the inner blocks (BI) and outer blocks (BO) are provided with a fine groove (6,7), of which the groove width being 0.01 to 0.07 times the ground contacting half width W, extending substantially straight in the tyre circumferential direction. A pneumatic tyre according to claim 1, 2 or 3, characterised in that the outer lateral grooves (go) of each outer block row (LO) extend parallel to each other, and the outer lateral grooves of one outer block row are inclined in the same direction with the outer lateral grooves of the other outer block row. A pneumatic tyre according to any of claims 1 to 4, characterised in that the inner lateral grooves (gi) are smoothly consecutive to every other outer lateral groove (go) of the adjacent outer block row (LO), and the inner lateral grooves (gi) have a bending point (5), at which the inner lateral groove (gi) inverts the inclination direction to the tyre circumferential direction, in the inner block row (LI). A pneumatic tyre according to any of claims 1 to 5, characterised in that the angle 1 at the acute side of the outer lateral grooves (go) crossing the groove edge (4) of the outer main grooves (GO) is in a range of 30 to 90 degrees, and the angle 2 at the acute side of the inner lateral grooves (gi) crossing the groove edge (3) of the centre main groove (GI) is in a range of 15 to 70 degrees.

Inventors: MINAMI NOBUAKI, MINAMI, NOBUAKI
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LTD.
Application year: 1994
Main classification: B60C11
IPC codes: B60C11